Hydro-pneumatic jet injector

Abstract

A pneumatic jet injector for needleless injection of a liquid medicine into the skin includes a pistol-shaped casing including a barrel, a handle and a trigger; a compression chamber in one end of the casing for a gas which is partially liquefied under pressure; a first piston movable in the casing against the gas; a charging liquid in the handle which is pumped against the first piston using the trigger and a second piston in the handle; a piston rod movable in the barrel with the first piston for creating a partial vacuum in the barrel for drawing medicine into the barrel through an inlet containing a one-way valve; a discharge orifice in one end of the barrel for discharging medicine into the skin of a user; and a safety catch in the handle for locking the first and second pistons in the loaded or charged position, and for releasing the pistons whereby at least a portion of the liquid in the compression chamber becomes gaseous moving the piston rod against the medicine to discharge the medicine through the orifice into the skin, while the charging liquid returns to the handle.

We claim: 
     
       1. A jet injector for administering a fluid medicine through the skin comprising: (a) an elongated tubular casing;   (b) handle means substantially perpendicular to said casing;   (c) plug means in said casing, said plug means dividing the interior of said casing into a medicine chamber and a compression chamber, said compression chamber containing a substance which is gaseous at normal room temperature and which converts to a liquid when subjected to pressure;   (d) an inlet duct in said casing for introducing medicine into said medicine chamber;   (e) a discharge orifice in said casing for discharging medicine from said medicine chamber into the skin;   (f) first piston means slidably mounted in said compression chamber for movement from a rest position toward said substance to a charged position, and away from said substance to the rest position;   (g) first rod means connected to said first piston means slidable in said plug means and extending into said medicine chamber for drawing medicine into and discharging medicine from said medicine chamber;   (h) a charging chamber in said handle means containing a charging liquid;   (i) a pressure chamber between said plug means and said piston means for receiving liquid from said charging chamber for pressing the first piston means against the substance;   (j) second piston means in said handle means;   (k) trigger means connected to said casing for moving said second piston means against said charging liquid, whereby said charging liquid is caused to pass from said charging chamber into said pressure chamber to move said first piston means against the substance to the charged position for liquefying a portion of said substance, and to cause said first rod means to move partially out of said medicine chamber for drawing medicine into the medicine chamber;   (l) safety catch means in said handle means for locking said first and second piston means in the charged position, and for releasing said first and second piston means to cause said first rod means to force said medicine through said discharge orifice while the charging liquid is returned to the charging chamber.   
     
     
       2. A jet injector according to claim 1, wherein said casing includes a rear handle end portion on one side of said plug means carrying said handle means and defining said compression chamber, and barrel means on the other side of said plug means defining said medicine chamber. 
     
     
       3. A jet injector according to claim 2, wherein said barrel means is releasably connected to said plug means. 
     
     
       4. A jet injector according to claim 3, wherein said first rod means includes one piston rod connected to said first piston means and slidable in said plug means and a second piston rod releasable connected to said one piston rod and slidable in said barrel for drawing medicine into and discharging medicine from said medicine chamber. 
     
     
       5. A jet injector according to claim 1, including adjustable stop means on said first rod means for varying the stroke of said first rod means and consequently the dosage of medicine drawn into said medicine chamber. 
     
     
       6. A jet injector according to claim 1, wherein said trigger means is pivotally connected to said casing for gripping with said handle means. 
     
     
       7. A jet injector according to claim 6, including first valve means in said handle means between said charging chamber and said pressure chamber; bar means slidably mounted on said handle for movement by said trigger means; and sleeve means in said handle means connected to said second piston means for moving the second piston means against said charging liquid. 
     
     
       8. A jet injector according to claim 7, wherein said sleeve means is mounted on said safety catch means for movement in one direction with said bar means and second piston means to press the second piston means against the charging liquid and for free sliding movement in the reverse direction. 
     
     
       9. A jet injector according to claim 8, including spring means for returning said sleeve means in the reverse direction, whereby said trigger means can be pumped to cause reciprocating movement of said bar means and sleeve means.